The gyroscopic integrating accelerometer was first disclosed in U.S. Pat. No. 1,940,387, "Gyroscopic Pendulum". The gyroscopic integrating accelerometer has a purposely unbalanced spinning gyroscope wheel that develops pendulous torque when it is accelerated along the input axis. The device then develops gyroscopic torque to balance out the pendulous torque. The angle of precession is proportional to the integral with respect to time of the acceleration along the input axis. Accordingly, by detecting the change in angle of the spin axis, the device is useful for determining acceleration along the input axis.
The concept of the pendulous integrating gyroscope was further developed after World War II. The pendulous integrating gyroscope accelerometer incorporates a purposely unbalanced, viscously damped, single degree of freedom gyroscope. The unbalance or pendulosity is made by offsetting the gyro wheel or by adding a pendulous mass along the spin axis. The pendulosity torque acting on the torque summing member of the gyroscope, caused by gravity or a specific force input such as acceleration, is counterbalanced by gyroscope precessional torque acting on the torque summing member in the opposing direction as a result of the rotation of the gyroscope about its input axis. The velocity of the gyroscope rotation is a direct indication of the acceleration being sensed. This device has a threshold sensitivity in the nano gravity range, and an operational range of 8 to 10 orders of magnitude.
There are a number of problems with the pendulous integrating gyroscope accelerometer, however, that have kept it from becoming an inexpensive, small, mass-producible device that can be used in commercial applications as opposed to defense and government applications in which cost is less of an issue. First, the rotating gyroscope wheel must be supported by bearings that will eventually wear. Additionally, the device requires a slip ring assembly to transfer power and excitations to the gyroscope assembly. This is another major failure mode associated with pendulous gyroscopic accelerometers. The devices also have a large number of parts which require extensive precision machining and assembly time. They also require a heavy viscous fluid for flotation and damping, and low viscosity fluid to partially float the weight of the gyroscope assembly and to lubricate the slip rings and bearings, both of which add to the number of assembly steps and thus the cost. Other problems with the device include the relatively large size and weight and the relatively large amount of operating power required to rotate the momentum mass and gyroscope assembly.